We are investigating the possible influence of fixed membrane surface charges on the mechanism for the quantal release of transmitter at the frog neuromuscular junction and of catecholamines from the frog adrenal. Surface charge density will be altered by changing intracellular pH or by the action of salicylates, which bind to the nerve membranes. We are also studying the effects of Ca ionophores, as a method for testing the widely-accepted hypothesis that neurohumor release follows an increase in intracellular Ca levels.